如何避免每次回发都重新加载GridView数据？

Question

I have a GridView which loads some data on Load like this:

protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        if (!Page.IsPostBack)
        {
            DataTable dataSource = LoadObjects();
            gvObjects.DataSource = dataSource;
        }
    }

I've also added a SelectedIndexChanged event handler where I want to perform some functions whenever a row is selected. The problem is that unless I remove the IsPostBack check from the OnLoad method, when a row is selected the GridView.SelectedRow attribute is not the row I selected.

Ideally I don't want to load all my data from the database on each postback. Are there any best-practices to get the selected row during the SelectedIndexChanged event without reloading everything again?

Thanks.

Answer 1

By default the GridView selects a row based on Index. Try instructing the GridView to select rows based on Keys.

Set the EnablePersistedSelection property to true so that the row selection is based on data-key values. Now if your earlier selected row gets its index or position changed in any way it will remain selected.

Answer 2

I usually have my GridViews full of dynamic controls which can be a lot of "fun", if they're not recreated on PostBack they don't work.

You seem only interested in the SelectedRow but this solution will also work and help save you a headache if you start getting fancy with dynamic controls

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);

    gvObjects.DataSource = LoadCachedObjects();
    gvObjects.DataBind();
}


private DataTable LoadCachedObjects()
{
    var result = new DataTable();
    if ((Session["CachedDataTable"] != null) && (IsPostBack))
    {
        //cached DataTable will only be used on PostBack
        result = Session["CachedDataTable"] as DataTable;
    }
    if (result.Rows.Count == 0)
    {
        result = LoadObjects(); //Get data from the database
        Session["CachedDataTable"] = result;
    }
    return result;
}

This only loads the data from the session when a postback event occurs, so you'll have one initial database hit on page load. Also if you end up using that code on other pages you don't have to be massively concerned about giving the session variable a unique name

Answer 3

If you can't prevent postbacks, you will obviously have to reload. So the solution would be to try to reload as little as possible.

A good way is to cache data somewhere, for example in the Session object. But only cache the primary keys together with a result index (1 to total result count). This way, you can quickly retrieve the primary keys that you need data for, and get only that data freshly from the database.